Outlook for Monday, September 28

Note on Medium Range Outlooks

You are looking at an outlook that is part of the medium range forecast (the outlook for days 4-8). The most important thing to note is that
lack of a risk does not mean zero risk.
Generally speaking, confidence has to be pretty high for the Storm Prediction Center to have an outlook area this far into the future.

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ZCZC SPCSWOD48 ALL ACUS48 KWNS 210852 SPC AC 210852

Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0352 AM CDT Mon Sep 21 2020

Valid 241200Z – 291200Z

DISCUSSION

Depending on the progression of Tropical Cyclone Beta, some severe threat may persist over parts of the lower MS Valley on Day 4/Thursday as it moves northeastward and merges with a weak mid-level trough. Considerable uncertainty exists regarding Beta’s placement, and the marginal forecast shear/instability across the lower MS Valley suggest no severe probabilities are warranted at this time.

Farther west, an upper trough should advance eastward from the Pacific Northwest to the northern/central Plains on Day 5/Friday. Low-level moisture is forecast to gradually increase ahead of this upper trough across parts of the Plains into the Upper Midwest and MS Valley. Warm mid-level temperatures may keep the warm sector capped across the Upper Midwest through much of the day Friday, although deep-layer shear is forecast to be rather strong.

An isolated/marginal severe risk may exist this upcoming weekend ahead of a cold front across a fairly broad portion of the CONUS extending from parts of the southern Plains to the Great Lakes. However, details remain unclear regarding the timing/amplitude of the eastward-moving upper trough and related surface features. Depending on this upper trough’s evolution, some severe risk may continue across parts of the eastern CONUS into early next week. Regardless, far too much uncertainty exists to include 15% severe probabilities at this extended time frame.

..Gleason.. 09/21/2020

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